This invention relates to an intake system for engines and more particularly to an intake system that improves the engine induction efficiency, particularly at low and medium speeds.
It has been acknowledged that the charging efficiency of an internal combustion engine, particularly at low and medium speeds is not particularly good. This results in reduced engine performance and occurs as a result of the successive starting and stopping of the induction charge downstream of the throttle valve as the intake valve or intake port is sequentially opened and closed. Each time the intake valve or port is open the inertia of the stopped intake charge must be overcome and the poor charging efficiency results. This problem is particularly prevalent in two-cycle engines.
It has recently been discovered that these difficulties with low speed charging efficiency may be significantly overcome by providing a plenum chamber that communicates with the intake system downstream of the throttle valve. The use of such a plenum chamber provides a volume in which vacuum is exerted at the point of closure of the intake valve or intake port which vacuum causes a continuous flow even after the valve or port is closed. This results in a more uniform flow through the intake passage, even at low speeds, and charging efficiency is improved. The theory behind this concept and several embodiments of incorporating it are disclosed in the copending application of Noritaka Matsuo et al. entitled Intake System for Engine, Ser. No. 163,201, filed June 25, 1980 and assigned to the assignee of this application.
Although the systems disclosed in that application are particularly effective in improving running at low speeds, particularly when the throttle valve has a relatively small opening, it has been found that in some conditions the use of the plenum chamber may actually deteriorate engine performance. This condition seems to occur when the throttle valve is at a fairly widely open position but the engine is still running at a relatively low speed.
It is, therefore, a principal object of this invention to provide an improved induction system for an internal combustion engine.
It is another object of this invention to provide an engine induction system that improves performance throughout all facets of the engine operation.
It is another object of this invention to provide an improved engine induction system through the use of a plenum chamber and by controlling the communication of the plenum chamber with the intake system.